1. Field of the Invention
The present invention relates generally to systems and methods for making and dispensing chemical solutions for use in conjunction with internal combustion engines. The present invention relates more specifically to systems and methods for making a dilute chemical solution from a liquid solvent (water) and either a dry composition (urea) or a concentrated solution (urea), at a point immediately prior to dispensing the dilute solution into a vehicle powered by an internal combustion (diesel) engine.
2. Description of the Related Art
Efforts are continuously being made to reduce emissions associated with the burning of hydrocarbon fuels in internal combustion engines. At the same time, efforts are being made to increase the fuel efficiency of these internal combustion engines. Recent efforts to improve the fuel efficiency of diesel engines have been successful but often at the cost of increasing emissions, especially nitrogen oxide ( ) emissions.
There are a variety of nitrogen oxide ( ) reducing systems that have been and currently are being developed for use in conjunction with diesel engines. One of these reducing systems is a urea based reducing solution, one type of which is marketed under the trade name AdBlue®. These systems are designed to reduce the pollutant emissions associated with the burning of diesel fuel in vehicular engines. These reducing systems were developed in response to a number of the newer processes that give diesel engines greater fuel economy but which as a result create extra emissions of certain pollutants. High compression ratios and lean air-fuel mixtures result in higher combustion temperatures, which in turn result in more nitrogen oxides and particulate matter being released into the gaseous exhaust system. While the particulate matter may typically be controlled with higher injection pressures and particulate filters, limiting the emissions can be more problematic.
One basic process for reducing emissions involves the injection of an aqueous urea solution (AUS) from a stored container on the vehicle into the exhaust stream. This process initiates a chemical reaction which, in conjunction with an additional catalytic converter, converts a significant percentage of the into water vapor and nitrogen. In general, the first stage catalytic converters utilized in conjunction with diesel engines initially trap the and later release it into a second converter which then converts it into nitrogen ( ) and water ( ). This basic system removes much of the, but through the addition of ammonia ( ) in the form of the AUS, a more complete conversion can be achieved. In other words, the exhaust system associated with a diesel engine will typically first include a diesel oxidation catalyst which reduces the amounts of carbon monoxide and hydrocarbons released from the exhaust. A catalytic converter begins the initial removal of oxides of nitrogen. Subsequently, a particulate filter traps and stores soot particles, burning them off when the filter gets full. Finally, in addition to the above, a selective catalytic reduction (SCR) catalytic converter takes the remaining nitrogen oxides and converts them to nitrogen and water by the addition of the AUS injected into the exhaust stream to enable the conversion.
A typical variety of AUS marketed under the trade name AdBlue® comprises AUS32 (aqueous urea solution 32.5%) and is used in the above described process referred to as selective catalytic reduction (SCR) to reduce emissions of oxide and nitrogen from the exhaust of diesel vehicles. This particular AUS solution is a 32.5% solution of high purity urea in demineralized water that is clear, non-toxic, and generally safe to handle. However, the solution can be corrosive for a number of metals and must be stored and transported using containers, conduits, valves, and fittings made up of certain non-corrosive materials. The AUS is typically carried onboard SCR equipped vehicles in specially designed tanks and is dosed into the SCR system at a rate typically equivalent to three to five percent of diesel consumption. This low dosing rate ensures long re-fill periods and minimizes the special tank's impact on chassis space. On highway SCR systems are currently in use throughout much of Europe, Australia, New Zealand, and the Far East.
The U.S. Environmental Protection Agency (EPA) 2010 legislation, which sets new limits on emissions, will, because of these new limits, require North American trucks to be equipped with SCR systems after 2010. In North America the AUS type reducing agent is commonly referred to as diesel exhaust fluid (DEF). A number of trucking industry manufacturers have already developed branded SCR systems that use aqueous urea solutions such as a product marketed under the brand name BlueTec®.
Most SCR systems currently in use and in development tend to be sensitive to chemical impurities in the urea solution. It is therefore important that high standards of quality are maintained for the composition that is delivered into the vehicle and for the delivery system itself. In general (and more specifically, throughout Europe), the use of SCR technologies has initiated a supply infrastructure that provides delivery of the manufactured solution to service stations that likewise provide the diesel fuel for the vehicles. In general, the sale and delivery of the AUS is made in canisters of five or ten liters, although larger quantities are sometimes delivered in two hundred liter drums. Deliveries to fueling depots are sometimes made in bulk tankers, not unlike the delivery of the diesel fuel itself.
In any case, the delivery of the AUS to a fuel station or depot where it is finally delivered to the vehicle that uses it is almost always made in liquid form, i.e., already mixed into a dilute solution. Unfortunately, it is this dilute solution that provides the most corrosive composition to the various metals that it might come into contact with and which requires the use of special storage containers and dispensing conduits. In contrast, the urea in its dry condition is relatively easy to transport and requires little in the way of special handling. In a similar manner, urea in a concentrated liquid condition can significantly reduce transportation cost, simply by reducing the quantity that must be transported (and the associated packaging).
It would be desirable, therefore, to deliver the much less corrosive compound, namely the dry urea powder or pellets, to a point where it might be stored without as significant a concern for its corrosive effects. Alternatively, it would be desirable to deliver the highly concentrated solution of urea to a point where it might be stored in much more manageable quantities. It would be desirable if the aqueous urea solution (AUS) could then be mixed and manufactured on-site to be immediately dispensed into the vehicle that will utilize the reducing agent. It would be desirable if this mixing of the dilute solution and the subsequent dispensing of the dilute solution could occur on an as-needed basis as opposed to requiring the maintenance of a supply that degrades over time, and potentially causes corrosive effects throughout the storage and delivery system. It would be desirable to avoid and/or minimize shipping and handling contamination risks and costs associated with the distribution of a solution versus the on-site manufacturing (blending) thereof.